dictionary of dictionaries

[kettle]

On Dec 10, 6:58 pm, Peter Otten <__pete... at web.de> wrote:
> kettle wrote:
> > On Dec 9, 5:49 pm, Marc 'BlackJack' Rintsch <bj_... at gmx.net> wrote:
> >> On Sun, 09 Dec 2007 00:35:18 -0800, kettle wrote:
> >> > Hi,
> >> >  I'm wondering what the best practice is for creating an extensible
> >> > dictionary-of-dictionaries in python?
>
> >> >  In perl I would just do something like:
>
> >> > my %hash_of_hashes;
> >> > for(my $i=0;$i<10;$i++){
> >> >     for(my $j=0;$j<10;$j++){
> >> >    ${$hash_of_hashes{$i}}{$j} = int(rand(10));
> >> >     }
> >> > }
>
> >> > but it seems to be more hassle to replicate this in python.  I've
> >> > found a couple of references around the web but they seem cumbersome.
> >> > I'd like something compact.
>
> >> Use `collections.defaultdict`:
>
> >> from collections import defaultdict
> >> from random import randint
>
> >> data = defaultdict(dict)
> >> for i in xrange(11):
> >>     for j in xrange(11):
> >>         data[i][j] = randint(0, 10)
>
> >> If the keys `i` and `j` are not "independent" you might use a "flat"
> >> dictionary with a tuple of both as keys:
>
> >> data = dict(((i, j), randint(0, 10)) for i in xrange(11) for j in xrange(11))
>
> >> And just for completeness: The given data in the example can be stored in a
> >> list of lists of course:
>
> >> data = [[randint(0, 10) for dummy in xrange(11)] for dummy in xrange(11)]
>
> >> Ciao,
> >>         Marc 'BlackJack' Rintsch
>
> > Thanks for the heads up.  Indeed it's just as nice as perl.  One more
> > question though, this defaultdict seems to only work with python2.5+
> > in the case of python < 2.5 it seems I have to do something like:
> > #!/usr/bin/python
> > from random import randint
>
> > dict_dict = {}
> > for x in xrange(10):
> >     for y in xrange(10):
> >         r = randint(0,10)
> >         try:
> >             dict_dict[x][y] = r
> >         except:
> >             if x in dict_dict:
> >                 dict_dict[x][y] = r
> >             else:
> >                 dict_dict[x] = {}
> >                 dict_dict[x][y] = r
>
> You can clean that up a bit:
>
> from random import randrange
>
> dict_dict = {}
> for x in xrange(10):
>     dict_dict[x] = dict((y, randrange(11)) for y in xrange(10))
>
>
>
> > what I really want to / need to be able to do is autoincrement the
> > values when I hit another word.  Again in perl I'd just do something
> > like:
>
> > my %my_hash;
> > while(<FILE>){
> >   chomp;
> >   @_ = split(/\s+/);
> >   grep{$my_hash{$_}++} @_;
> > }
>
> > and this generalizes transparently to a hash of hashes or hash of a
> > hash of hashes etc.  In python < 2.5 this seems to require something
> > like:
>
> > for line in file:
> >   words = line.split()
> >   for word in words:
> >     my_dict[word] = 1 + my_dict.get(word, 0)
>
> > which I guess I can generalize to a dict of dicts but it seems it will
> > require more if/else statements to check whether or not the higher-
> > level keys exist.  I guess the real answer is that I should just
> > migrate to python2.5...!
>
> Well, there's also dict.setdefault()
>
> >>> pairs = ["ab", "ab", "ac", "bc"]
> >>> outer = {}
> >>> for a, b in pairs:
>
> ...     inner = outer.setdefault(a, {})
> ...     inner[b] = inner.get(b, 0) + 1
> ...>>> outer
>
> {'a': {'c': 1, 'b': 2}, 'b': {'c': 1}}
>
> and it's not hard to write your own defaultdict
>
> >>> class Dict(dict):
>
> ...     def __getitem__(self, key):
> ...             return self.get(key, 0)
> ...>>> d = Dict()
> >>> for c in "abbbcdeafgh": d[c] += 1
> ...
> >>> d
>
> {'a': 2, 'c': 1, 'b': 3, 'e': 1, 'd': 1, 'g': 1, 'f': 1, 'h': 1}
>
> Peter

Nice, thanks for all the tips!  I knew there had to be some handier
python ways to do these things.  My initial attempts were just what
occurred to me first given my still limited knowledge of the language
and its idioms.  Thanks again! -joe